My PhD program is 'on hold' as well. It's been 15 years, but someday I plan to get back to it.<p>Depending on who I talk to, I say "I found I liked programming better than my research", "I grew distrustful that the simulation methods were meaningful", "I wasn't getting the support I needed from my adviser; I was one of 14 students and he traveled a lot", and "I was doing too much CS for a physics degree, and too much physics for a CS degree. Only in retrospect years later did I realize that I was actually interested in molecular informatics." (I've spent the last 20 years working in structural informatics, bioinformatics, and chemical informatics.)<p>I don't think you understand the difference between undergraduate and graduate schools. Grad school is more like a job. You don't "drop out" of working for McDonald's, you quit, and explore other interests.<p>Also, it's not like leaving graduate school is uncommon. Attrition rates in graduate school (math and physical science) are 25% within the first four years. See <a href="http://www.insidehighered.com/news/2007/12/07/doctoral#sthash.cPpxTdm0.dpbs" rel="nofollow">http://www.insidehighered.com/news/2007/12/07/doctoral#sthas...</a> , and after 10 years of graduate school only 57% end up with a degree.<p>See also <a href="http://chronicle.com/article/PhD-Attrition-How-Much-Is/140045/" rel="nofollow">http://chronicle.com/article/PhD-Attrition-How-Much-Is/14004...</a> , "She rejects the term "dropout" to describe someone who leaves graduate school. I agree with her that the word "connotes individual failure" when someone may simply be departing for a better opportunity."